Motor control system

ABSTRACT

A motor control system including a modulator consisting of a saturable reactor, a magnet means and a control means. The magnet means produces a magnetic flux to be supplied to the reactor, which is controlled by the control means, so that the switching means is controlled through the magnet means by the saturable reactor.

United States Patent [1 307/88 LL, 88 P 11] 3,7353% Uemura 51 May 22,1973 [541 MOTOR CONTROL SYSTEM [56] References Cited [75] Inventor:Saburo Uemura, KanazaWa-ku, UNITED STATES PATENTS Yokohama, Japan3,627,896 12/1971 Uemura ..3l8/l38 [7 3] Asslgne ny C p ra n, T y apan3,529,220 9 1970 Kobayashi. .....318/138 3,466,519 9/1970 Platnick..3l8/l38 [221 Flledl 14, 1972 3,452,262 6/1969 Mogzala ..3l8/l38 [211pp NO 225 923 3,439,243 4/1969 Roth ..3l8/l38 Primary Examiner-BernardA. Gilheany [30] Foreign Application Priority Data AssistantExaminerTh0mas Langer Att0rney-Lewis H. Eslinger, Alvin Sinderbrand andFeb. 13, 1971 Japan ..46/6323 Curtis, Morris & safford Feb. 13, 1971Japan ..46/6324 [57] ABSTRACT [52] US. Cl ..318/l38, 307/88 LC A motorcontrol System including a modulator Consist [51] Int Cl 02k 29/00 ingof a saturable reactor, a magnet means and a con- 01 means The magnetmeans produces a magnetic 58 Field of Search ..318/138, 254, 439; fluxto be Supplied to the reactor, which is Controlled by the control means,so that the switching means is controlled through the magnet means bythe saturable reactor.

18 Claims, 32 Drawing Figures Patented May 22, 1973 3,735,216

9 Sheets-Sheet 1 Patented May 22, 1913 3,735,216

9 Shets-Sheet 5 MAfiNE T16 FIELD A m w Patented May 22, 1973 9Sheets-Sheet 5 Patented May 22, 1973 9 Shee tS-ShGG t 7 $3 MAIINETICFIELD I I I I I -m-: VOLTAGE 0 M CURRENT Iii j- J1 Patented May 22, 19733,735,216

9 Sheets-Sheet 8 Patented May 22, 1973 3,735,216

9 Sheets-Sheet 9 Ii g- 15B jig-15D V V V V- MOTOR CONTROL SYSTEMBACKGROUND OF THE INVENTION 1. Field of the Invention This inventionrelates to an improved motor control system using saturable reactors.More particularly it relates to an improved simple motor control systemfor varying rotating speed of a motor or reversing the rotation thereofor both.

2. Description of the Prior Art One known technique for controlling therotating speed of a motor is to vary the gate angle of siliconcontrolledrectifiers connected to field coils of the motor. There is no problem ifthe rotor rotates in only one direction. However, it is impossible forthe siliconcontrolled rectifiers to change the rotational direction ofthe rotor continuously from one direction to the reverse direction,because the silicon-controlled rectifiers are one-way rectifierelements. Therefore, two sets of silicon-controlled rectifiers androtating position detecting devices are required for each of the fieldcoils to change the direction of rotation of the motor. The requirementfor two rectifiers for each field coil makes it impossible tomanufacture such a motor at a low cost.

Another way of controlling switching circuits in field coils is by meansof saturable reactors. The saturable reactors are excited by anoscillator and outputs of the reactors are varied by the positioning ofthe rotor, whereby the positioning of the rotor can be detected. Usingthis approach, it is possible to manufacture a low cost motor. However,no consideration is given to changing the direction of rotation of therotor continuously from one direction to the reverse direction.

There is still another system for deriving a control signal from asignal having a frequency proportional to the rotation numbers of therotor from a signal generator individual to the rotor in order tomaintain a DC motor at a predetermined rotating speed. In such a system,if the rotating speed of the rotor is faster than the predeterminedrotating speed, the frequency of the signal generator increases. Thenthe increment signal corresponding to the increased frequency is fedback to a control circuit connected to a motor power source to reducethe power to be supplied to the motor. On the other hand, when therotating speed of the rotor is slower than the predetermined rotatingspeed, the signal of the frequency generator decreases. Then, thedecrement signal is fed back to the control circuit to cause more powerto be supplied to the motor. In this motor control system, the motor hasa long lifetime, because the rotating speed of the rotor can be detectedwithout any mechanical contact due to the use of the frequencygenerator. This system has a disadvantage that smooth operation of thecontrol circuit cannot be effected under transient conditions, becausethe power lines are directly turned on and off. Further, in this motorcontrol system a signal output signal of the frequency generator isconverted into a direct voltage signal through a filter and a rectifier,the direct voltage signal is compared with a reference voltage, and thena control signal is produced based on the comparison. Therefore, whenthe motor is driven at a slower rotating speed, lack of accuracy isintroduced into the voltage comparison because ripple components aresuperposed upon the detected output. Since the motor control circuit isdirectly controlled by the control signal derived from a comparisoncircuit, it is necessary to provide means for eliminating the mutualinterference of a drive circuit and the control circuit in the motorcontrol system.

It is, therefore, a general object of this invention to provide animproved motor control system which eliminates the above-describeddisadvantages.

Another object of this invention is to provide an improved motor controlsystem having saturable transformers which act as saturable reactorssuitable for detecting the rotating position of the motor and can easilydetect the positioning of the rotor.

Another object of this invention is to provide an improved motor controlsystem which is adapted to control the motor speed by varying thestrength of the biasing magnetic field applied to saturable transformersacting as saturable reactors.

Still another object of this invention is to provide an improved motorcontrol system wherein a linear relation is established between acontrol current for controlling the motor speed and a load currentflowing through the motor so that the motor control may be easily made.

Still another object of this invention is to provide an improved motorcontrol system wherein the motor can be controlled by separating motorspeed controlling means from a load circuit for the motor in directsignal.

A further object of this invention is to provide an improved motorcontrol system in which the motor can be continuously and smoothlychanged from one direction to the reverse direction by varying thedirection of the biasing magnetic field applied to saturabletransformers acting as saturable reactors for detecting the rotatingposition of the rotor.

A still further object of this invention is to provide an improved motorcontrol system which is low in cost and easy to handle.

SUMMARY OF THE INVENTION This invention is directed to a motor controlsystem wherein switching circuits are provided at a motor connected to apower supply, and the switching characteristic of the switching circuitsis varied by the outputs of the saturable reactors having a controlmeans. High frequency gating signals are coupled through the transformeronly when the transformer is not saturated. A biasing field saturatesthe transformer and is reduced or canceled by a reverse field, and thenet biasing determines the amount of coupling. The transformer outputsignal is used to gate rectifying semiconductors.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit diagram showing abrushless motor incorporating a motor control system according to thisinvention FIG. 2 is a perspective view of a saturable transformer andbiasing magnet means of a type that may be used in the motor controlsystem of FIG. 1.

FIG. 3 is a graph for explaining the operation of the saturabletransformer shown in FIG. 2.

FIG. 4 is a circuit diagram showing a portion of the circuit in FIG. 1.

FIGS. 5A-5I are waveforms showing signals occurring in the saturabletransformers and currents flowing through field coils of the motors inFIG. 1.

FIGS. 6A6D show wave forms typical of operation of the circuit in FIG.1.

FIG. 7 is a graph showing difference voltage and high frequency signalssupplied to a width modulator in relation to an output characteristiccurve of the width modulator.

FIG. 8 is a circuit diagram showing a second embodi ment of thisinvention.

FIGS. 9 through 11 are graphs for the explanation of the operation ofthe embodiment of FIG. 8.

FIG. 12 is a circuit diagram showing a third embodiment of thisinvention.

FIG. 13 is a graph for explaining the operation of the embodiment inFIG. 12.

FIG. 14 is a circuit diagram showing a fourth embodiment of thisinvention.

FIGS. 15A-15G are graphs for explaining the operation of the embodimentin FIG. 14.

DESCRIPTION OF THE PREFERRED EMBODIMENTS I -are wound around statorcores surrounding the rotor 1 in the proximity of the periphery of therotor l and are angularly spaced from one another by 120. One end ofeach of these field windings 2a, 2b, and 2c is connected to a commoncenter tap of a secondary winding of a transformer 3. An alternatingsignal from a commercially available power supply (not shown) is appliedacross both ends 30 and 3b of the primary winding of the transformer 3.One end of the secondary winding of the transformer 3 is connected tothe respective anodes of silicon-controlled rectifiers 4a, 4b, and 4c(hereinafter referred to as SCRs) and the other end of the secondary isconnected to the respective anodes of SCRs 4a, 4b, and 4c The cathodesof the SCRs 4a and 4a are connected to each other and to the other endof the field coil 2a, the cathodes of the SCRs 4b and 4b are connectedto the other end of the field coil 2b, and the cathodes of the SCRs 4cand 4c are connected to the other end of the field coil 20.

A magnetic field generator 5 is connected mechanically to the rotor l torotate therewith. The magnetic field generator 5 comprises a magneticdisk permanent magnet in which flat portions are formed on oppositesides leaving rounded ends which are oppositely magnetically polarized.Three saturable transformers 6a, 6b, and 6c acting as saturable reactorsare angularly spaced from one another by l20 around the periphery of themagnetic field generator 5 similarly to the field coils 2a, 2b, and 20.

FIG. 2 is one example of a saturable reactoroa. This reactor includes acore 7 made of a magnetic'material having low coercive force, forexample a ferrite or the like. The core 7 comprises two magnetic fluxconvergence portions 8a and 8b for converging external magnetic flux,and the core 7 also comprises two magnetic flux saturable portions 9aand 9b having smaller crosssectional areas than those of the magneticflux convergence portions 8a and 8b. A primary winding 10a is woundaround the magnetic field saturable portion 9a and a secondary winding11a is wound around the magnetic field saturable portion 9b. Thesaturable transformer 6a straddles the legs of a yoke 12, around which abias coil 13 is wound. The yoke 12 and the bias coil 13 form a magneticfield generator.

When an external positive magnetic field is applied to the saturabletransformer 60, as shown in FIG. 3, so that the magnetic flux density ofthe core 7 reaches +Hs (for example, 2,000 Gauss), the saturableportions 9a and 9b become saturated with magnetic flux. As a result, thevalues of inductances of the primary and secondary windings 10a and 11abecome very small, resulting in reduction of the coupling coefficient ofthese windings from about I to 0.1 or less. Therefore, a small outputvoltage is produced by the secondary winding 11a. Here the saturabletransformer 6a has a characteristic such that an output signal isproduced across the secondary winding 11a of the saturable transformer6a when the transformer is operating in an area I, shown in FIG. 3, butnot when it is operating in an area II. In the following description,the area I will be referred to as the on area, and the area II will bereferred to as the off area. It will be understood that when currentflows through the bias coil 13 of the saturable transformer 6a toproduce a positive biasing magnetic field +Hb higher than the saturationmagnetic field I-Is and a magnetic field developed by the magnetic fieldgenerator 5 is further applied to the bias coil 13, an output signal isdeveloped from the secondary winding 11a of the transformer 6a duringone revolution of the magnetic field generator 5 and for the time duringwhich a negative magnetic field is applied thereto, as shown in theshaded area of FIG. 3. As stated above, the magnetic field generator 5is not circular-shaped but is squared off at both sides. Thus, since themagnetic field of the magnetic field generator 5 is inclined during acertain interval, the on time period of the saturable transformer isdetermined by varying the value of the biasing magnetic field and is,for example,

which is very efficient for the motor.

When a negative magnetic field is applied to the saturable transformer,the saturable transformer presents on and off characteristics in theareas I and II, respectively, in a manner similar to the case ofapplication of the positive magnetic field. Therefore, it will beunderstood that when the negative magnetic field -Hb is applied byreversing the direction of the biasing current supplied to the biaswinding 13, an output signal is developed from the secondary winding ofthe transformer during one revolution of the magnetic field generator 5and for the time during which the magnetic field shown in the shadedarea of FIG. 3 is applied thereto. It will be noted that this on" timeperiod is different from that of application of the positive magneticfield with respect to rotating phase of the magnetic field generator.

The two other saturable transformers 6b and 6c are similar to thesaturable transformer 6a. The primary windings 10a, 10b, and 100 ofthese saturable transformers 6a, 6b, and 6c are connected to form aseries circuit, one end of which is connected to an output terminal ofan amplifier 14 and the other end of which is grounded. Further, one endof the secondary winding 11a of the saturable transformer 6a isconnected to the gates of SCRs 4a and 4a, one end of the secondarywinding 11b of the saturable transformer 6b is connected to the gates ofSCRs 4b and 4b, and one end of the secondary winding 110 of thesaturable transformer 6c is connected to the gates of SCRs 4c and 4c.The other ends of these secondary windings 11a, 11b and 110 areconnected to the center tap of the transformer 3.

A high frequency signal from an oscillator 16 is supplied to anamplifier 14 and is width modulated by a width modulator 15 to which asinusoidal wave voltage from a sinusoidal oscillator 17 is applied. Thecomparison output derived from a comparison circuit 18 is also applied,in the form of an absolute value, to the sinusoidal wave oscillator 17through a diode bridge 19. The comparison output results in a differencevoltage in which an output voltage corresponding to the level androtating position, which are set in response to the rotating speed ofthe rotor l, is substracted from a set reference voltage correspondingto the desired rotating position and rotating direction. Here aconventional tachometer 20 may be used to measure rotational speed ofthe rotor 1.

FIG. 4 shows one embodiment of a combination of the width modulator 15,the comparison circuit 18, and the diode bridge 19. The comparisoncircuit 18 is a differential amplifier, the base of one transistor 18awhich is connected to the arm of a potentiometer across which positiveand negative DC voltages are applied so that the reference voltage maybe formed at the arm. The output of the tachometer 20 is connected to abase of the other transistor 18b thereof through a terminal 20a.Collectors of both of these transistors 18a and 18b are connected to thediode bridge 19 to derive a difference signal therefrom, the differencesignal being impressed across a winding 22a wound around one leg of aU-shaped yoke of magnetic material. A signal voltage is applied to awinding 22b wound around the other leg of the yoke. A saturable core 23is placed so that it straddles the space between the legs of the yoke.The high frequency oscillator 16 is connected to a primary winding ofthe saturable core 23, and the output derived from a secondary windingthereof is supplied to the amplifier 14. The width modulator 15comprising the yoke and the saturable core may be similar inconstruction to corresponding parts shown in FIG. 2.

FIG. I also shows that the comparison output of the circuit 18 issupplied to a determination circuit 24 for determining whether thecomparison output is positive or negative. A bias signal source 25 iscontrolled depending upon the result of the determination. Thus, whenthe comparison output is determined to be positive, a positive biasingsignal is applied to respective biasing windings of the saturabletransformers 6a, 6b, and 60.

In the operation of the foregoing circuits, the output signal of thehigh frequency oscillator 16 is supplied to the primary windings of thesaturable transformers 6a, 6b, and 6c, and a positive biasing magneticfield is applied to these saturable transformers. When the highfrequency oscillator 16 is operated to supply an alternating signal tothe transformers 6a, 6b, and 60 through the modulator 15, only thesaturable transformer 6a is turned on, because the proper opposing flux(N-S, N is shown in the figure) is effected from the upper surface ofthe magnetic field generator 5 to the lower surface.

This causes a high frequency signal H,, which is shown in FIG. 5A, to besupplied to the gates of the SCRs 4a and 4a through the saturabletransformer to obtain a full-wave rectified output R shown in FIG.

5D, which is supplied to the field coil 2a. Thus, a north pole isinduced in the field winding 2a, whereby the rotor 1 rotates in thedirection of the arrow a (FIG. I).

Since the magnetic field generator 5 rotates with the rotor 1, thesaturable transformer 6b is next turned on, whereby a high frequencysignal H shown in FIG. 5B, is supplied to gates of the SCRs 4b and 4b toobtain a full-wave rectified output R as shown in FIG. 5E, which issupplied to the field winding 212, thus permitting the rotor 1 to rotatefurther in the direction of the arrow a because of introduction of anorth pole in the field coil 2b. Similarly, since the saturabletransformer 6c is next turned on, a high frequency signal H is suppliedto gates of the SCRs 4c and 40', as shown in FIG. SC, to obtain afull-wave rectified output R shown in FIG. 5F, which is supplied to thefield coil 2c. Thus, the rotor l rotates through the transferring of thefield current.

Control of the direction of rotation of the brushless DC motor can beeffected by displacing the on time period of each of the saturabletransformers 6a, 6b, and 60 by or reversing the direction of currentsflowing through the field coils 2a, 2b, and 20. There are two ways ofreversing the direction of currents flowing through the field coils.According to one way, a relay is used. According to the other way, twosets of SCRs are used. In the former, some mechanical contacts areindispensable. In the latter, two sets of SCRs and detectors arerequired for positive and negative directions with the result that theconstruction is complex.

In this invention, transferring of the biasing magnetic field from onevalue (for example, +I-Ib) to the other value (-Hb) causes the on timeperiod of each of these saturable transformers 6a, 6b, and 6c to bedisplaced by 180 in phase. Further, control of the rotating speed of thebrushless DC motor is effected by applying a positive or negative driveforce with respect to the rotating direction to produce the requiredacceleration or deceleration.

Operation of the circuit to control the rotating direction and rotatingspeed in one embodiment of this invention will be described next. FIG.6A shows a voltage waveform in which a signal voltage is superposed upona difference voltage signal E supplied to the winding 22a of the widthmodulator 15 (FIG. 4) from the comparison circuit 18. Since the widthmodulator 15 presents an output characteristic with respect to anexternal magnetic field, as shown in FIG. 7, it is turned on during oneperiod of one component of the signal wave and the time perioddetermined by the difference voltage signal. On and off conditions ofthe width modulator 15 are shown in FIG. 6B. Therefore, a high frequencysignal HE is obtained from the output of the width modulator 15, thehigh frequency signal being intermittently width modulated as shown inFIG. 6C by the difference signal and supplied to the primary windings ofthe saturable transformers 6a, 6b, and 6c.

A SOI-Iz AC is gated with the width modulated high frequency signal asshown in FIG. 6D. The high frequency'signal I-IE (shown in FIG. 6C) issupplied to gates of the SCRs in such a manner that it is sequentiallytransferred by the turning on and off of the saturable transformers 6a,6b, and 60, as shown in FIGS. 5A, 5B, and 5C. This width modulationresults in the absolute difference voltage signal between the detectionoutput of the tachometer 20 and the reference voltage signal, that is,the amount of acceleration,

which is independent of negative and positive. The determination will bemade by the determination circuit 24. When the detection output of thetachometer 20 is larger than the reference voltage signal, for example,the difference signal is determined to be negative. In this case, anegative biasing signal is supplied to the saturable transformers 6a,6b, and 6c from a signal source 25, whereby the on time period of eachof the saturable transformers is displaced by 180. Thus the rotor lrotating in the direction of the arrow a is subject to the reversetorque (that is, the direction of the arrow b) resulting in thedeceleration thereof. On the contrary, when the detection output of thetachometer 20 is smaller than the reference voltage signal, a positivebiasing magnetic field is applied to the saturable transformers 6a, 6b,and 60, whereby they are subjected to the normal torque (that is, thedirection of the arrow a). Thus, the rotating speed is controlled tohave a value corresponding to the reference voltage signal.

Reversal of the rotor from the direction of the arrow a into thedirection of the arrow b is effected by displacing the on time period ofeach of the saturable transformers 6a, 6b, and 6c by 180 from therelationship shown in FIGS. 5A, 5B, and SC to that in FIGS. SO, SB, andSI. Thus, a high frequency signal H is applied to the gates of SCRs 4aand 4a through the turning on and off of the transformer 60 at the timesshown 1 in FIG. 5G. Similarly, a high frequency signal H is applied tothe gates of SCRs 4c and 4c through the turning on and off of thetransformer 60 at the times shown in FIG. 5H, and a high frequencysignal H is applied to the gates of SCRs 4b and 4b through the turningon and off of the transformer 6b at the times shown in FIG. SI.Therefore, when the rotor l is to rotate in the direction of the arrowa, a positive biasing magnetic field +Hb is applied to each of thesaturable transformers 6a, 6b, and 60. Conversely, when the rotor l isto rotate in the direction of the arrow b, a negative biasing magneticfield Hb is applied to each of the saturable transformers 6a, 6b, and6c.

As will be apparent from the above description, according to theabove-described embodiment constant speed control is effected bymodulating the time period during which current flows through the fieldwindings 2a, 2b, and 2c in response to the detection output which isdependent on whether the motor speed is faster or slower than thepredetermined speed set by the reference voltage. Further, accelerationor deceleration of the motor is accomplished by displacing the on timeperiod of each of these saturable transformers by 180". Therefore, twosets of SCRs is not needed for positive and negative directions. Thus,the construction of this embodiment is very simple.

FIG. 8 shows another embodiment according to this invention in which anAC voltage from a commercially available power supply, that is, SOI-Iz,100v, is supplied across input terminals 101a and llb. The inputterminal 101a is connected through a capacitor 102 to one end of awinding 104 mounted on a core 103, and the other end thereof isconnected to a grounding terminal l0lb. A control winding 105 is woundaround the core 103, and the ends of this winding are connected toterminals 106a and 106b to which a control signal is applied, forexample a DC current for controlling voltage supplied to field coils ofthe motor. Here the core 103 and the windings 104 and 105 form a magnetmeans.

When an alternating voltage e is applied to the input terminals 101a and101b,

e E sinwt (where, E is constant) the alternating current i supplied tothe winding 104 is out of phase with respect to the alternating voltageThat is to say,

i l coswt (where, I is constant) A saturable transformer 108 is disposedopposite the open end of the yoke 103. The construction andcharacteristics of the saturable transformer 108 are similar to those ofthe saturable transformers shown in the first embodiment. A primarywinding 103a is wound around a saturable core 109 and both ends of thiswinding are connected to a high frequency oscillator 114 for supplying ahigh frequency signal, for example a IOO-SOOKI-Iz high frequencycurrent. A secondary winding l03b wound around the saturable core 109 isconnected to a load.

A load motor substantially similar to the motor described in the firstembodiment is shown in FIG. 8. The motor comprises a rotor 110 that hasnorth and south poles magnetized around it, a magnetic field generator111 adapted to rotate with the rotor 110, three field windings 112a,112b, and l12c surrounding the rotor 110, three saturable transformers113a, 113b, and 113c associated with respective field windings anddisposed along the periphery of the magnetic field generator 1 l1, andthree SCRs adapted to switch current flowing through said respectivefield windings. One end of each of the field windings is connected tothe input terminal 101a and the other end of each winding is connectedto the input terminal 101b through cathodes of the SCRs'. The saturabletransformers 113a, 113b, and 113C are similar in construction andcharacteristics to those of the first embodiment. One coil 116a, 116b,

and 116C wound around each of the saturable cores a, 115b, and 1150 isconnected across the gates and cathodes of corresponding SCRs 114a,114b, and 114s. The other coils 117a, 117b, and 1170 on the cores 115a,115b, and 115s are connected in series to one another and are connectedacross the coil l03b of the first saturable transformer 108.

The operation of the second embodiment will now be described. Assumingthat the coupling coefficient magnetic field characteristic of thesaturable transformer 108 is shown in curve A of FIG. 10 wherein when amagnetic field applied to the saturable transformer 108 is between +8and B the coils 103a and 103b of the saturable transformer 108 aremagnetically coupled to each other. This allows a high frequency signalapplied from the high frequency oscillator 114 to the coil 103a to becoupled to the coil l03b. When the magnetic field is more than +8 orless than B the coupling is much lower and the signal cannot be obtainedfrom the coil 103b. The magnet means comprising the yoke 103, thewinding 104, and the control winding 105 develops a magnetic field Bwhen a direct current flows through these windings.

An alternating current i is applied to the winding 104, where i l coswtA control current I for example, is applied to the control winding 105.

In this case, when currents i and I, flowing through the winding 104 andthe control winding 105, respectively, of the magnet means exceed apredetermined current 1 the saturable transformer 108 becomes saturatedwith magnetic flux, so that the output signal cannot be obtained fromthe coil l03b. Thus, the load or motor is controlled by determiningwhether the currents I and iflowing through the windings 104 and 105 arelarger or smaller than the current I,,.

That is to say, when the following relation is established as shown inFIG. 10:

an output signal can be obtained from the coil 1031) of the saturabletransformer 108. On the contrary, when the relation is established, anoutput signal cannot always be obtained from the coil 103b of thesaturable transformer 108.

Thus, when the following relation is true,

an output signal may be obtained from the coil 103b of the saturabletransformer 108 within a certain angle range of the current i l coswt,that is, i I I,, and an output signal is not developed therefrom withinthe other angle range, that is, I I I,,.

The output of the saturable transformer 108 controlled by the value ofthe control current I, is supplied to coils 117a, 117b, and 11% of thesaturable transformers 113a, 113b, and 113C which are spaced around themagnetic field generator 111. When a north pole portion N of themagnetic field generator 111 approaches the saturable transformer 113a,this saturable transformer 113a couples the output of the oscillator 114to the gate of SCR 114a through the coil 116a, resulting in turning onof the SCR 114a. Thus, current of positive half cycles flows through thefield winding 112a. Similarly, when the north pole N of the magneticfield generator 111 rotates close enough to the saturable transformer113b, this transformer 1l3b is turned on, whereby SCR 1l4b is turned on,thus permitting current of positive half cycles to flow through thewinding 112b. When the north pole N of the magnetic field generator 111is opposite the saturable transformer 113e, this transformer 1130 isturned on, whereby the SCR 114:: is turned on, thus permitting currentof positive half cycles to flow through the winding 1120. Thus, therotor 110 is rotated in the direction of the arrow a. The rotating speedis determined by the timing of the turning on of each of the SCRs. Itwill, of course, be understood that the timing is determined by thecurrent value of the control current 1,.

As is well known in the art, current flows through each of the SCRsduring the positive half cycles of the voltage supplied to anodes of theSCRs. That is to say, current flows through each of the SCRs during thepositive half cycles within the phase range between the gating angle 0and 180, where 0 is the phase at which a trigger voltage is supplied toeach of the SCRs during the positive half cycles. At this time, thephase 0 by which each of the SCRs is turned on and off is determined bythe following equation:

Thus, 0 can be obtained by solving the above equation.

That is,

0 cos"(l,, 1 /1 On the contrary, the integration value 1,, of a directcurrent flowing through each of the SCRs is as follows.

(where, I is constant) By putting equation l) into equation (2), thefollowing equation is obtained.

IOHCA i" "117 Therefore, it will be easily understood that theintegration value of the direct current is in proportion to the controlsignal 1 That is to say, a linear relationship is established betweenthe integration value 1,, of the direct current flowing through each ofthe SCRs and the control current as shown in FIG. 11, which means that alinear relationship is established between a load current and thecontrol current according to this invention.

Further, according to the second embodiment of this invention, the powersupply and the SCRs are con nected by transformers to a circuit forsupplying a control current and an oscillator. Therefore, they arecompletely separated from each other insofar as a direct signal isconcerned, and they are not adversely affected by each other.

When a SOOKHZ high frequency signal is developed from the high frequencyoscillator 114 in the above-described embodiment, the coils 103a and103b of the saturable transformer 108 have less turns, whereby theimpedance of the saturable transformer 108 is low. As a result, each ofthe SCRs is triggered in a stable condition, because the gate-cathodeimpedance of each of the SCRs is low.

FIG. 12 shows a third embodiment in which the motor can rotate in eitherdirection. In FIG. 12, current flows through a control winding 205 inone direction to control a saturable transformer 208, while currentflows through a control winding 205' in the reverse direction to controla saturable transformer 208'. Biasing windings 216 and 216 are providedin the neighborhood of cores 203 and 203', respectively. When currents(1,, 1 flow through the biasing windings 216 and 216' as biasingcurrents, a linear relation is established between a load current I(average current) and a control current I, over the positive andnegative areas of the load current as shown in FIG. 13. Further, a highfrequency signal current from a high frequency signal source 214 issupplied to respective windings 213a and 213a of the saturabletransformers 208 and 208', the other windings 213k and 2l3b' of whichare connected to gates of a pair of SCRs 215 and 215'. Connected acrossthe input terminals 201a and 201b are a capacitor 202 and coils 204 and204' which are wound in the reverse relation to each other and connectedto cores 203 and 203'. An armature 207 for the motor is also connectedbetween the terminals. Therefore, according to the third embodimentshown in FIG. 12, the positive and negative rotations and the rotatingspeed of the DC motor can be controlled by the control current impressedacross the control terminals 206a and 206k. It will be, of course,understood that the third embodiment is similar to the second embodimentin its technical effect.

FIG. 14 shows a fourth embodiment wherein the phase of thebi-directional current of the alternating current can be controlled byonly one saturable transformer and a magnet means as shown in the fourthembodiment of FIG. 14.

In FIG. 14, input terminals 301a and 3011) are connected to a full-waverectifier 317, and a clipper circuit 318 comprising a resistor 318a anda Zener diode 318b is connected between two output terminals of thefullwave rectifier 317. The junction between the resistor 318a and theZener diode 318b is connected to the base of a switching npn transistor320 through a capacitor 319 forming a part of a difierential circuit.Further, the base of the transistor 320 is grounded through a diode 321for deriving a negative-going signal, shown in FIG. 15E, from the outputof the capacitor 319 forming a part of the differential circuit. Theemitter of the transistor 320 is grounded and an integration circuit 322comprising a resistor 322a and a capacitor 322b is connected across theoutput terminals of the full-wave rectifier 317. Output terminals of theintegration circuit 322 are connected between the collector of thetransistor 320 and ground and is also connected across a winding 304 ofa magnet means.

The input terminals 301a and 30lb are also connected across a primarywinding 323a of a transformer 323 which has two secondary windings 323band 323b wound in the reverse relation to each other. A common junctionof the secondary windings 323b and 323b is connected to one end of amotor 307 and the other ends thereof are connected to the anodes of SCRs315 and 315 whose cathodes are connected to the other end of the motor307. A secondary coil 313b of a saturable transformer 308 is connectedto the gates of the SCRs 315 and 315.

Wound around a core of the saturable transformer 308 is a primarywinding 313a to which a high frequency signal current from a highfrequency signal source 314 is supplied. Also wound around a core 303 ofthe magnet means is a control coil 305 to which a control current issupplied.

According to the above-described construction, voltage waveforms whichare 180 out of phase with each other as shown in FIGS. 15A and 15B areobtained from the secondary windings 323b and 323b of the transformer323. Therefore, voltages corresponding to positive and negative cyclesof the input power source voltage are applied to SCR's 315 and 315.

The input signal is fully rectified by the full-wave rectifier 317 asshown in FIG. 15C and is clipped by the clipper circuit 318 to provide aclipped voltage waveform having a predetermined level as shown in FIG.151). The clipped voltage is supplied to the integration circuit 322 andthe capacitor 319 forming a part of the differential circuit. Thewaveform differentiated by the capacitor 319 is shown in FIG. 15E. Onthe other hand, the voltage clipped by the clipper circuit 318 isapplied to the capacitor 322b to form a sine curve. However, when apredetermined time elapses the capacitor 319 is discharged, because theoutput of the capacitor 319 is applied to the base of the transistor320. As a result, a voltage shown in FIG. 15F is supplied to the winding304 of the core 303. Therefore, when the control current 1 as shown inFIG. 15F, is supplied to the control coil 305, the current flow angle ofcurrents flowing through SCRs 315 and 315' can be controlled by onesaturable transformer to produce the waveform shown in FIG. 15G.

What is claimed is:

1. A motor control system comprising: a rotor; a plurality of fieldwindings connected to a relatively low frequency power source; rotatablemagnetic flux producing means mechanically connected to said rotor; aplurality of saturable reactors adjacent said magnetic flux producingmeans; means for supplying a high frequency signal to said saturablereactors; a plurality of silicon-controlled rectifier switching meansconnected to said field windings, respectively, for controlling currentflowing through said field windings for intervals of time correspondingintervals that said high frequency signal is derived from the respectiveones of said saturable reactors; control means to produce a speed errorsignal; and means for modulating, in response to said speed error signalderived from said control means, the duration of time said highfrequency signal is supplied to said switching means.

2. A motor control system according to claim 1 wherein said modulatingmeans comprises a magnetic yoke and an additional saturable reactoropposite said magnetic yoke.

3. A motor control system according to claim 2 wherein said magneticyoke for said modulating means comprises: a biasing coil to receive analternating signal, and a control coil to receive said control signalfrom said control means; and said additional saturable reactorcomprises: a saturable core, a primary coil wound on said saturable coreto receive a high frequency signal from said means for producing a highfrequency signal, and means for transmitting the output of saidadditional saturable reactor to said plurality of saturable reactors.

4. A motor control system according to claim 3 comprising said highfrequency signal producing source, and means connecting said source tosaid primary coil.

5. A motor control system according to claim 2 wherein said additionalsaturable reactor comprises a transformer comprising a saturable core.

6. A motor control system according to claim 2 wherein said magneticyoke for said modulating means comprises a biasing coil to receive analternating current having a phase differing by a predetermined anglefrom the phase of a voltage to be supplied to said field windings, and acontrol coil to receive said control signal from said control means.

7. A motor control system according to claim 1 which further comprisesmagnetic bias means opposite said plurality of saturable reactors toapply a bias magnetic field to each of said plurality of saturablereactors.

8. A motor control system according to claim 1 wherein each of saidsaturable reactors includes a magnetic core and a biasing coil woundaround said magnetic core to receive a direct current from a powersource connected to said biasing coil.

9. A motor control system according to claim 8 comprising: a directcurrent source; and means to connect said source to said biasing coil ineither polarity to produce a biasing magnetic field of selectedpolarity.

10. A motor control system according to claim 1 which further comprises;a detector for detecting the rotating speed of said rotor; and comparingmeans for comparing the output of said detector with a reference valueto produce an error signal to be supplied to said control means.

11. A motor control system according to claim 10 wherein said controlmeans comprises a diode bridge, whereby the absolute value of said errorsignal is supplied to said modulating means as a control signal.

12. A motor control system according to claim 1 wherein said pluralityof saturable reactors comprises a plurality of transformers, eachincluding a saturable core.

13. A motor control system comprising: a rotor; a plurality of fieldwindings connected to a relatively low frequency power source forrotating said rotor; a magnetic flux producing means mechanicallyconnected to said rotor; a plurality of saturable reactors adjacent thepath of rotation of said magnetic flux producing means; means supplyinga high frequency signal to said saturable reactors; a plurality ofsilicon-controlled rectifier switching means connected to saidrespective field windings for controlling current through said fieldwindings corresponding to an output derived from a respective one ofsaid saturable reactors; magnet means for magnetically biasing each ofsaid saturable reactors; and means for changing over said magnetic fieldproduced by said magnet means from one polarity to the oppositepolarity.

14. A motor control system according to claim 13 wherein said magnetmeans comprises; a magnetic yoke; and a biasing coil wound around saidmagnetic yoke.

15. A motor control system according to claim 13 wherein said saturablereactors comprise; saturable cores; a primary winding wound around eachof said saturable cores to receive said high frequency signal; and asecondary winding wound around said saturable cores and connected to arespective one of said switching means.

16. A motor control system comprising a motor comprising a rotor andstator; a relatively low frequency alternating power source forsupplying alternating power to said motor; silicon-controlled rectifierswitching means connected to said power source for controlling currentflowing through said motor; a comparison circuit; a reference signalsource connected to said comparison circuit; means connected to saidcomparison circuit and operable for deriving a voltage corresponding tothe speed of said motor; means for producing a second current having apolarity determined by said derived voltage; a saturable reactor havinga coil to receive a high frequency signal and an output means forderiving output signals therefrom, said output means being connected tosaid switching means to actuate said switching means in response to asaturable condition of said saturable reactor; magnet means to receivesaid second current for producing magnetic flux and to supply saidmagnetic flux to said saturable reactor; and a control means provided atsaid magnet means for controlling the magnetic flux produced by saidmagnet means.

17. A motor control system according to claim 16 wherein said saturablereactor comprises; a saturable transformer having a saturable core; acoil wound around said saturable core to receive the high frequencysignal supplied from a high frequency signal producing source; and anoutput coil wound around said saturable core for supplying an output ofsaid saturable reactor to said switching means.

18. A motor control system according to claim 16 wherein said magnetmeans comprises: a magnetic yoke and a coil wound around said magneticyoke to receive said current; and a control coil wound around saidmagnetic yoke to receive a control direct current from said controlmeans.

1. A motor control system comprising: a rotor; a plurality of fieldwindings connected to a relatively low frequency power source; rotatablemagnetic flux producing means mechanically connected to said rotor; aplurality of saturable reactors adjacent said magnetic flux producingmeans; means for supplying a high frequency signal to said saturablereactors; a plurality of silicon-controlled rectifier switching meansconnected to said field windings, respectively, for controlling currentflowing through said field windings for intervals of time correspondingintervals that said high frequency signal is derived from the respectiveones of said saturable reactors; control means to produce a speed errorsignal; and means for modulating, in response to said speed error signalderived from said control means, the duration of time said highfrequency signal is supplied to said switching means.
 2. A motor controlsystem according to claim 1 wherein said modulating means comprises amagnetic yoke and an additional saturable reactor opposite said magneticyoke.
 3. A motor control system according to claim 2 wherein saidmagnetic yoke for said modulating means comprises: a biasing coil toreceive an alternating signal, and a control coil to receive saidcontrol signal from said control means; and said additional saturablereactor comprises: a saturable core, a primary coil wound on saidsaturable core to receive a high frequency signal from said means forproducing a high frequency signal, and means for transmitting the outputof said additional saturable reactor to said plurality of saturablereactors.
 4. A motor control system according to claim 3 comprising saidhigh frequency signal producing source, and means connecting said sourceto said primary coil.
 5. A motor control system according to claim 2wherein said additional saturable reactor comprises a transformercomprising a saturable core.
 6. A motor control system according toclaim 2 wherein said magnetic yoke for said modulating means comprises abiasing coil to receive an alternating current having a phase differingby a predetermined angle from the phase of a voltage to be supplied tosaid field windings, and a control coil to receive said control signalfrom said control means.
 7. A motor control system according to claim 1which further comprises magnetic bias means opposite said plurality ofsaturable reactors to apply a bias magnetic field to each of saidplurality of saturable reactors.
 8. A motor control system according toclaim 1 wherein each of said saturable reactors includes a magnetic coreand a biasing coil wound around said magnetic core to receive a directcurrent from a power source connected to said biasing coil.
 9. A motorcontrol system according to claim 8 comprising: a direct current source;and means to connect said source to said biasing coil in either polarityto produce a biasing magnetic field of selected polarity.
 10. A motorcontrol system according to claim 1 which further comprises; a detectorfor detecting the roTating speed of said rotor; and comparing means forcomparing the output of said detector with a reference value to producean error signal to be supplied to said control means.
 11. A motorcontrol system according to claim 10 wherein said control meanscomprises a diode bridge, whereby the absolute value of said errorsignal is supplied to said modulating means as a control signal.
 12. Amotor control system according to claim 1 wherein said plurality ofsaturable reactors comprises a plurality of transformers, each includinga saturable core.
 13. A motor control system comprising: a rotor; aplurality of field windings connected to a relatively low frequencypower source for rotating said rotor; a magnetic flux producing meansmechanically connected to said rotor; a plurality of saturable reactorsadjacent the path of rotation of said magnetic flux producing means;means supplying a high frequency signal to said saturable reactors; aplurality of silicon-controlled rectifier switching means connected tosaid respective field windings for controlling current through saidfield windings corresponding to an output derived from a respective oneof said saturable reactors; magnet means for magnetically biasing eachof said saturable reactors; and means for changing over said magneticfield produced by said magnet means from one polarity to the oppositepolarity.
 14. A motor control system according to claim 13 wherein saidmagnet means comprises; a magnetic yoke; and a biasing coil wound aroundsaid magnetic yoke.
 15. A motor control system according to claim 13wherein said saturable reactors comprise; saturable cores; a primarywinding wound around each of said saturable cores to receive said highfrequency signal; and a secondary winding wound around said saturablecores and connected to a respective one of said switching means.
 16. Amotor control system comprising a motor comprising a rotor and stator; arelatively low frequency alternating power source for supplyingalternating power to said motor; silicon-controlled rectifier switchingmeans connected to said power source for controlling current flowingthrough said motor; a comparison circuit; a reference signal sourceconnected to said comparison circuit; means connected to said comparisoncircuit and operable for deriving a voltage corresponding to the speedof said motor; means for producing a second current having a polaritydetermined by said derived voltage; a saturable reactor having a coil toreceive a high frequency signal and an output means for deriving outputsignals therefrom, said output means being connected to said switchingmeans to actuate said switching means in response to a saturablecondition of said saturable reactor; magnet means to receive said secondcurrent for producing magnetic flux and to supply said magnetic flux tosaid saturable reactor; and a control means provided at said magnetmeans for controlling the magnetic flux produced by said magnet means.17. A motor control system according to claim 16 wherein said saturablereactor comprises; a saturable transformer having a saturable core; acoil wound around said saturable core to receive the high frequencysignal supplied from a high frequency signal producing source; and anoutput coil wound around said saturable core for supplying an output ofsaid saturable reactor to said switching means.
 18. A motor controlsystem according to claim 16 wherein said magnet means comprises: amagnetic yoke and a coil wound around said magnetic yoke to receive saidcurrent; and a control coil wound around said magnetic yoke to receive acontrol direct current from said control means.